Can different osteotomies have an influence on surgically assisted rapid maxillary expansion? A systematic review

The purpose of this study was to systematically review the randomized and non-randomized clinical trials (RCT; nRCT) concerning the different available osteotomies for surgically assisted rapid maxillary expansion (SARME): pterygomaxillary disjunction (SARME + PD vs SARME-PD) and segmental Le Fort I osteotomy (2-piece vs 3-piece). Outcomes focused on skeletal, dental, upper airway changes, complications, and relapse. Two authors investigated five databases (PubMed, Cochrane Library, Google Scholar, Scopus, Web of Science) until August 2023. The Cochrane Collaboration Tool and the Newcastle–Ottawa scale were used for the quality assessment of the included RCTs and nRCTs, respectively. A total of 554 articles were retrieved and after duplicates removing and full-text reading, 40 studies were included. Two RCTs showed a low risk of bias, one an unclear risk and one a high risk. Among the non-RCTs, 15 studies showed a good quality, while 21 exhibited a fair quality score. SARME + PD resulted in more homogeneous posterior bone expansion, with minimal dental effects. No difference between 2-piece and 3-piece in asymmetric expansion was observed, although 3SO showed 1–2 mm of more transverse increase. The oropharynx minimum cross-sectional area, the nasopharynx and the oropharynx volume were greater in SARME + PD. Both dental and bone relapse can occur but no differences between the groups were observed. All osteotomies guaranteed a correction of transverse maxillary deficiency. Lower side effects were described in SARME + PD. Two-piece and 3-piece segmental Le Fort I osteotomies did not show any differences in the symmetry and amount of expansion. Supplementary Information The online version contains supplementary material available at 10.1186/s13005-024-00415-3.


Introduction
Transversal maxillary discrepancies represent a common type of malocclusion among young and adult people with an incidence range of 8-18% of patients requiring orthodontic evaluation [1].The resulting crossbite can be distinguished according to the causal factor: in most cases a maxillary constriction is outlined, at other times a maxillary constriction is associated with an increased mandibular width but sometimes a normal maxillary transverse dimension is associated with an increased mandibular width [2].A multifactorial etiology can be recognized for transversal maxillary deficit, including congenital, developmental (thumb sucking, breathing alterations), iatrogenic (cleft palate repair), or traumatic factors [3,4].When a diagnosis of maxillary constriction occurred, it's useful to improve the transversal discrepancy, to increase the arch perimeter for a correct dental alignment and arch coordination, to enlarge the palatal vault providing an adequate space for the tongue, and to increase the nasal cavity width for the improvement of nasal breathing [5,6].
In patients with skeletal maturity, surgically assisted rapid maxillary expansion (SARME) is indicated for the treatment of extreme transverse maxillary hypoplasia [2,7].Orthodontic therapy can camouflage discrepancies less than 5 mm (mm) with orthopedic forces alone, but when a higher transversal maxillary discrepancy occur, SARME is considered the gold standard [8].
To date, there is no consensus in the literature for the best osteotomies to be performed in SARME.All maxillary joints and suture lines have been found to contribute differently to resistance to maxillary expansion [3,5,[9][10][11][12][13][14][15][16][17][18][19].The areas of resistance have been classified as anterior support (piriform aperture pillars), lateral support (zygomatic buttresses), posterior support (pterygoid junctions), and median support (midpalatal synostosed suture) [2,20].As clinical consequence, the surgical procedure can include Le Fort I osteotomy in association with other specific osteotomies: 1) pterygomaxillary disjunction (PD); 2) median palatal suture osteotomy that can be defined as segmental 2-piece osteotomy (2S); 3) two paramedian osteotomies between the lateral incisor and the canine (3-piece; 3S).In order to choose the best treatment, to guarantee the best predictable and stable results, to achieve the minimal patient morbidity, and to avoid complications and relapse at the long-term, more details on maxillary osteotomies for SARME are needed [1,5,12,16,[21][22][23].It is essential to focus on which osteotomies could decrease any resistance to maxillary expansion, achieving an adequate transversal correction without periodontal damage [5].
The purpose of this study was to systematically review the available randomized and non-randomized clinical trials to analyze the different osteotomies used in SARME in terms of skeletal, dentoalveolar, upper airways outcomes, relapse, and complications.

Materials and methods
A systematic review was conducted following PRISMA guidelines and PICOS (participants, intervention, comparisons, outcomes, and study design) criteria: (P) Human participants of any age, sex, and ethnicity, (I) diagnosed with transverse maxillary deficiency equal to or greater than 5 mm, exhibiting a mono-or bilateral crossbite, (C) included in randomized-and non-randomized-clinical trials (O) that evaluated the various osteotomies employed in SARME in terms of skeletal, dentoalveolar, upper airway outcomes, relapse, and complications.

Search strategy and study selection
The PubMed, Cochrane Library, Google Scholar, Scopus, Web of Science databases were investigated up to August 2023 for the electronic search.The term sequence used in PubMed search was: "((maxillary expansion[MeSH Terms]) AND (osteotomy, le fort[MeSH Terms])) AND (orthognathic surgery[MeSH Terms])", "(((maxillary expansion[MeSH Terms]) AND (orthognathic surgery[MeSH Terms])) AND (segmental osteotomy)", "(((maxillary expansion[MeSH Terms]) AND (orthognathic surgery[MeSH Terms])) AND (pterygomaxillary disjunction)) OR (segmental le fort I osteotomy)", "((orthognathic surgery[MeSH Terms]) AND (le fort osteotomy[MeSH Terms])) AND (2-piece or 3 piece)".The term sequences used in the other search databases were: "[surgically assisted rapid maxillary expansion] AND [pterygomaxillary disjunction] OR [segmental le fort I osteotomy]", "(("maxillary expansion") AND (segmental AND le AND fort AND I AND osteotomy) OR (pterygomaxillary AND disjunction))", "("maxillary expansion") AND (segmental le fort I osteotomy) OR (pterygomaxillary disjunction)".To complete the search strategy, a manual search was performed, considering the reference lists of the included studies.No restriction of language or publication date was applied.
The electronic search was conducted independently by two investigators (SB and MS).The screening of titles and abstracts allowed to assess the randomized-and non-randomized-clinical trials (RCT; nRCT) for eligibility (Fig. 1).Full-text reading was scheduled when missing information persisted.Any disagreement between the two authors were discussed with an expert supervisor (AG).The inter-rater reliability between the two investigators (SB and MS) was determined calculating the Cohen's kappa coefficient (k).

Data extraction process
Data extraction was separately performed by the same two authors (SB and MS) from eligible studies.The recorded data were the following: author, publication date, country of the included studies, number of the included patients, type of intervention, methodological procedure, outcomes, studies' results, and author's conclusion.

Assessment of methodological quality
The analysis of the methodological quality was independently conducted by the two investigators (SB and MS).Each included RCT was evaluated using the Cochrane Collaboration Tool [24].The Cochrane Collaboration Tool is a validated instrument, assessing the study design and methodology according to six domains (selection bias, performance bias, detection bias, attrition bias, reporting bias, other bias).Each domain expresses the risk of bias in the format "low", " "high", or "unclear".Nonrandomized clinical trials were assessed using the Newcastle-Ottawa Quality Rating Scale.Each study can show poor, fair, or good/high quality based on a star rating system with eight elements in three domains (selection, comparability, and outcome) [25].

Study selection
maxillary expansion had no significant difference between A total of 554 articles were retrieved from five databases.The duplicates were then removed, leaving a total of 273 articles.The articles were then screened on the basis of title and abstract and 58 articles were selected (Suppl.Tab. 1).After a full-text analysis, 18 articles were dismissed because they related to other topics.A total of forty 40 articles were finally included in the systematic review (Table 1).The inter-rater agreement coefficient was k = 0.91.
A total of 1513 adult patients with transverse maxillary deficiency greater than or equal to 5 mm, with a mono-or bilateral crossbite, were treated under general anesthesia [5, 6, 26, 27, 29-37, 39-48, 50, 51, 54-59,   The cross-sectional area of the maxilla was significantly increased.The angle between the anterior nasal spine and the inferior margin of the alveolar bone increased in a significant manner (P G 0.05).
A statistically significant increase in maxillary width was also observed in the intermediate portion of the maxilla.Measurements of the distance between the right and left greater palatine foramina, and the angle between the anterior nasal spine and the greater palatine foramina did not show differences that were statistically significant.
No complications; All patients spontaneously reported a clinically significant improvement in nasal airflow and breathing.
Fair tooth mesio-palatine cusp) In the SARPE group, the increase in the intercanine distance between T1 and T2 ranged from 4.5 to 10.5 mm, whereas the change from T2 to T3, or the relapse, ranged from + 1 to -6 mm.Similarly, the intermolar distance increased by 5-9.5 mm between T1 and T2, whereas the relapse ranged from + 3 to -3.5 mm In the Le Fort I bipartition group, the increase in the intercanine distance ranged from 0 to 4.5 mm, which was smaller than that in the SARPE group, whereas the relapse ranged from + 3.5 to -2.5 mm.In contrast, the intermolar distance was increased by 2.5-7.5 mm, and the relapse ranged from 0 to -5 mm.The differences throughout T1-T3 for both treatments were significant (p < 0.001).The relapse in the intercanine and intermolar distances between T3 and T2 was smaller for Le Fort I bipartition than for SARPE.

Good
Table the distance between the right and left vestibular gingival margins.
the distance between the right and left palatal gingival margins For transverse dental maxillary widening: the distance between the right and left vestibular cusp tips the distance between the right and left palatal cusp tips.
-  -Distance between the second premolar furcation points bilaterally.
-Distance between the first molar furcation points bilaterally.
-Angulation of the alveolar crests.
-Vertical molar movement.Periodontal measurement -Width of the buccal alveolar bone in the canine region.
-Width of the buccal alveolar bone in the first premolar region.
-Width of the buccal alveolar bone in the second premolar region.
-Alveolar bone height in the canine region.
-Alveolar bone height in the first premolar region.
-Alveolar bone height in the second premolar region.
-Alveolar bone height in the first molar region.Anterior skeletal expansion was evident in both groups with no statistically significant differences between them.At the dentoalveolar level, significant expansion was obtained between contralateral teeth (P0.01), with no significant differences between the 2 groups.More pronounced tipping, without statistical significance, was reported in SARME + PD group.
On the dental level, all distances between cusps of the contralateral teeth increased significantly in both groups with no difference between the groups.SARME resulted in buccal tipping of all posterior teethbut not of the canines.
On the periodontal level (Table VIII), the width of buccal alveolar bone decreased for all posterior teeth in both groups.
The height of the alveolar crest was reduced more in the SARME-PD group in the premolar area, but the difference did not reach statistical significance.
Fair There was a significant difference in the intercanine distance between the 2-piece and 3-piece SARME groups at T2, T3, and T4 (P < .001):2-piece osteotomy showed higher values at any timings.
No significant difference between the 2-piece and 3-piece SARME groups was found in the inter-Second Molar Distancesat (P > .05).
No significant difference between the 2-piece and 3-piece SARME groups was found in the Skeletal Jugulum Distance (P > .05).In both the SARME-PD and SARME + PD groups, the greatest expansion occurred at the dental arch, followed by palatal bone and nasal floor level, all the differences were statistically significant (P < 0.0001).

Good
In both the SARME-PD and SARME + PD groups, the amount of expansion achieved at the first premolar and molar areas was comparable, indicating a parallel widening of maxilla postero-anteriorly.
Fair No differences were found between the groups in the expansion of dental and skeletal measurements (P > 0.05).However, changes over time were significant for all measures (P < 0.001).Significant differences between time points T2 and T3 were found for the distance between the palatal root apices in molars, intermolar angle, nasal floor width at the level of premolars, and interpremolar angle.A recurrence of nasal floor width (0.29 mm) was observed between T2 and T3.
The distance of the root apices of the first molars increased by 1.28 mm during the retention period (P < 0.001).Increases of tooth tipping were observed after expansion of molars and premolars as a result of SARME, with a decrease in these angles was observed between T2 and T3 (P < 0.05).
The amount of expansion in the cusps of the first molars was similar to that obtained in the cusps of the first premolars (P = 0.632), with a parallel expansion occurred when evaluated at the coronal level of the teeth supporting the appliance.Similar results were found for measurements at the level of the palatal root apex (P = 0.315).
The results revealed greater expansion in the lowest region of the maxilla; these results translate to a tilt of the maxillary segment.
Quantitative analysis of the included studies could not be performed, considering the large difference in the outcomes' assessment.

Assessment of quality
About the RCTs, the analysis of the methodological quality showed a low risk of bias in two articles [58,63].One study reported a high risk of bias [36].An unclear risk of bias was recorded for one RCT [50].The most critical items of the Cochrane Collaboration Tool were in the selection bias and reporting bias (Fig. 2).Among the non-RCTs, 15 studies showed a good level of quality, while 21 exhibited a fair quality score (Table 2) [5, 6, 26, 27, 29-35, 37, 39-48, 51, 54-57, 59, 61-68].

Skeletal outcomes
Pterygomaxillary disjunction All studies reported a significant transversal increase in the maxilla [5,6,31,36,38,45,54,58,[61][62][63]65].According to pterygomaxillary disjunction, a more homogeneous maxillary expansion is achieved in SARME + PD [5,36,58,61,63].The anterior maxillary segment recorded a higher expansion in SARME -PD, confirming the V-shaped sutures opening, showing a posterior expansion lesser than 0.5 mm compared to SARME + PD [36,54,58,63].SARME-PD showed a differential expansion in the anterior and posterior part of the maxilla up to 3 mm [5].Greater expansion was observed at the anterior region than the posterior region [65].However, Lauderman and colleagues stated that PD seemed to have an effective role in patients older than 20 years, while adjunct benefits of this osteotomy were not analyzed in younger subjects [36].Craniocaudal analysis showed a greater expansion in the alveolar bone than in the palatine level, with a difference up to 2 mm [5,6,45,54,65].Immediately after the activation period, the SARME + PD group showed a significant increase in the height of the middle and lower third of the face; however, these changes cancelled out during the stabilization phase, leading to a return to the initial condition [62].Concerning the direction of the bone movement, anteriorly to posteriorly there was an outward segmental inclination for SARME + PD and an inward one for SARME -PD [31,36].Asymmetric expansion could be achieved with a clinically relevant difference between right and left side (> 3 mm), more the anterior-inferior component than in the inferior-posterior component [6].In terms of transverse widening, bone-borne appliances showed a lower opening than tooth-borne devices but with a lower buccal tipping of the molars and an increased buccal bone plate at premolars, after both SARME + PD and -PD [36].
Segmental Le Fort I osteotomy According to segmental technique, eight studies described the skeletal outcomes between two-segments and three-segments osteotomies [36,58].No statistically significant difference between 2 and 3S was found in the asymmetry of the maxillary expansion [36,40,57,58].However, 3SO showed 1-2 mm of more transverse increase compared to 2SO and expanded more symmetrically [37,51,59].Also, Lauderman et al. reported a significative transverse widening higher than 2 mm in SARME + PD and segmental 3-piece osteotomy [36].During the postoperative orthodontic treatment period, the 2S group exhibited a significant decrease in the skeletal width [29,51].The greatest loss in vestibular bone substance was detected in the bipartite [29].Concerning the direction of the bone movement, a lateral bending was analyzed in SARME with 2S, while a medial bending was more frequent in 3-piece osteotomy [36].

Dentoalveolar outcomes
Pterygomaxillary disjunction Dental transformations were observed in CBCT images comparing prior to and following expansion, with an average expansion ranging from 6 to 9 mm [27,33,54,55,68].According to pterygomaxillary disjunction, dental tipping occurred preeminently in SARME -PD group.SARME + PD group showed a lower tendency of buccal molar tipping (≅ − 2 degrees) either after appliance removal or after 6 months follow-up [63].The major molar tipping in SARME -PD determined a molar expansion greater than 1 mm compared to SARME + PD, especially with a tooth-borne device.As reported by Laudemann and colleagues, dental tipping showed an outward tipping in TB devices and an inward tipping in BB devices, according to the different level of distraction at which the two devices act (BB at bone level; TB at dental level) [36].Most teeth in both groups ( SARME + PD and SARME -PD) exhibited a rise in crown height, though with not statistical significance [54].In SARME -PD group the dental expansion was higher than SARME + PD group, with a decreased degree of canine inclination when PD was not performed.However, when PD was performed, dental expansion was more in the anterior palatal region than in the posterior arch width [68].The SARME + PD group showed an increased but nonsignificant vestibular bone resorption in the second molar region and an increased palatal bone plate thickness on the first premolar.In contrast, at the premolar level a higher bone resorption was found in SARME-PD and a greater increase in vestibular bone plate thickness was decorded in the SARME + PD group when bone-borne devices were used [31].In terms of stability, Ferraro-Bezerra M. et al. assessed an increased distance between the buccal and palatal alveolar processes during the retention period [63].
Segmental Le Fort I osteotomy According to segmental technique, six studies reported the dentoalveolar outcomes between two-segments and three-segments osteotomies.Significantly more dental expansion was noted following 2-piece than 3-piece (P = 0.009) [40,51,57].Although the difference in the increase in the distance between the mesiopalatal cusps of the maxillary first molars was not significant between two groups (2S and 3S), a greater variation in the angulation of the first molar was found in the 2-piece group [59].Intermolar distance was found to Fig. 2 Risk of bias assessment for the included RCTs increase by 2.5-7.5 mm when bipartite Le Fort was performed, while at the intercanine level this increase was less [30].An augmented dental tipping was found in the 3-piece osteotomy, with a greater inward angulation for the central incisors and canines, while the lateral incisors went to a greater outward angulation [37].The different position of the post-operative diastema (between the central incisors in 2S; between the lateral incisors and the canines in 3S) showed a better psychological impact for patients undergoing to SARME with segmental 3-piece Le Fort I [58].The patients' perceptions of smile aesthetics after expansion were significantly different: the 2S group were clearly dissatisfied compared with 3S group [59].In assessing periodontal status, periodontal probing revealed that 100% of the postoperative measurements remained between 1 and 2 mm for the whole sample.Because this interval is totally compatible with periodontal health, no statistical test was deemed necessary to evaluate differences between both groups [59].

Upper airway outcomes
Pterygomaxillary disjunction According to PD, maxillary expansion improved nasal width and breathing [27,34,41,48,55].In their study, Romulo et al. performed several measurements (minimum cross-sectional area of the oropharynx (OMCSA), nasal cavity volume (NCV), sinus volume (MSV), nasopharynx volume (NPV), oropharynx volume (OPV), and total volume) before and after surgery in order to assess changes in upper airway volume.No statistically significant differences were recorded in the accumulated volume of the upper airways, although + PD group always showed higher values than -PD group at each follow-up [50].The analysis of the specific items showed that NPV and OMCSA were significantly higher in + PD group both after active expansion and after 6 months follow-up compared to the initial condition (p < 0.05).The OPV increased significantly in the + PD group compared to controls, but only after the active expansion follow-up (p = 0.007).Osteotomy with PD showed a significant increase in the postoperative alar base, maintained until 36 months after surgery [34,48].In patients treated with PD, no statistically differences were detected in the distances from the base of the pyriform aperture to the nasal septum between sides and in the position of the nasal septum in relation to the left and right lateral walls of the pyriform aperture [46].
Segmental Le Fort I osteotomy According to segmental osteotomies, Prado and colleagues showed an increased width of the nose in two-segments than three-segments technique, with a significant difference (p = 0.016).Furthermore, the superimposition of the facial scans showed a significantly larger transversal displacement of the paranasal area when horizontal osteotomy with the threesegment technique was performed (p = 0.014).No differences on vertical or anteroposterior axes were analyzed.

Complications and relapse
Only five studies reported data on post-operative relapse [30,37,57,58,63].According to PD, Ferraro-Bezerra et al. reported both dental and bone relapse in the anterior region during the retention period, either in SARME + PD or in SARME-PD [63].Comparing two-and three-segments osteotomies, Prado et al. performed a reintervention in two patients, one for each group, because of an unresolved asymmetrical expansion, however in their study in relation to skeletal stability, no relapse was assessed comparing area and volume of the palate vault both after removal of the expander and after follow-up 6 months; Da Costa reported relapse included unilateral posterior crossbite in 2 patients (6.2%) in the 3-piece and 2 patients (4.8%) in the 2-piece at 1 year postoperatively [57,58].Marchetti et al. found minimal recurrence in the intermolar distance when the bipartite Le Fort was performed, while at the intercanine level this increase was found to be smaller and with a higher recurrence rate [30].Transverse widening was associated with greater decline when 3-piece with pterygoid osteotomy was performed, and a bone-borne device was used [36,37].Because of infection, 9,4% of patients treated by Da Costa underwent a reintervention to remove osteosynthesis device.An asymmetric expansion occurred in three cases who required re-intervention by Alfaro et al., 2 patients of SARME + PD treated by Gursoytrak and 2 patients treated by Da Costa, 2 2SO cases by Landes [37,56,57].
Reported intraoperative complications included an osteotome-induced palatal mucosal laceration, which was sutured without postoperative dehiscence; two patients developed intraoperative hemorrhage with subsequent hematoma formation in the SARME + PD group; in the group without pterygoid osteotomy, only one patient had hemorrhage [56,67].Post-surgical complications were reported as hemorrhage and hematoma in two patients and infraorbital nerve paresthesia in four patients after SARME-PD, one patient and 12 patients, respectively, in SARME + PD group [43,56,67].
Sinus infections were reported by Cakarer when pterygomaxillary disjunction was not performed and by Da Costa in SARME + PD cases [57,67].Regarding bi-and tripartite osteotomies Landes and Da Costa documented cases of dental damage as discoloration [29,37,57].Pain was more prevalent in the 2-piece group, while complications such as bone resorption and gingival recessions were found in the 3-piece osteotomies [57].Complications often associated with smoking or noncompliance were noted, such as dehiscence, fistula, pain, headache, and distractor loosening.

Discussion
The purpose of this study was to systematically review the available randomized clinical trials concerning the different osteotomies that can be performed in surgically assisted rapid maxillary expansion.The analysis focused on skeletal changes, dentoalveolar modifications, upper airway variations, relapse, and complications to evaluate the best outcomes of this surgical procedure.
An ideal therapeutic approach for SARME should achieve the advantages of an efficient maxillary expansion, limiting the intraoperative and post-operative complications [69].An adequate balance between surgical goals and orthodontic aims is needed.Surgically, SARME should be performed with a simple technique, avoiding successive complications.From an orthodontic viewpoint, SARME should be effective in the transversal orthopedic correction, with a symmetric result, avoiding a post-therapeutic relapse or a periodontal damage of the upper teeth [64,70].So, the planned osteotomies should obtain the best result, minimizing the risks.The anatomical regions of major resistance for maxillary expansion are well known, including the posterior processes of the maxillary bone that articulate with the pterygoid processes of the sphenoid bone in a fixed joint, and the median suture of the palate that is a fixed linker between the right and left maxillary bones [71].On these perspectives, most authors concentrated their attention on the role of pterygomaxillary disjunction and median palatal osteotomy during SARME [44,59,[71][72][73].To summarize the evidence-based results, this review 1) analyzed the outcomes of SARME with or without PD, and 2) compared the clinical findings performing a segmental Le Fort I in 2-piece (2S) or 3-piece (3S) osteotomy.
Despite the different approach, all osteotomies allowed to achieve a correction of the transversal maxillary deficiency both in the short-and long-term follow-up [5, 6, 26, 27, 29-37, 39-48, 50, 51, 54-59, 61-68].With reasonable evidence, SARME + PD showed a more homogeneous skeletal expansion and, although without a significant difference, the anterior segments of the maxillary bone showed a greater transversal movement [58,63].Pterygomaxillary disjunction determined a greater posterior skeletal expansion compared to SARME -PD in which a V-shaped suture opening occurred with higher expansion in the anterior maxillary segment [58,63].As reported by Ferraro-Bezerra, at the long-term follow-up, palatal expansion at the molar region exceeded of 0.5 mm in SARME + PD compared to SARME -PD, despite the hyrax opening was lower than 0.4 mm in SARME + PD group [63].According to the biomechanical statement, the center of resistance located at the posterior part of the median palatal suture allowed a more parallel expansion when PD occurred because the increased expansion at the molar region was mainly related to the lateral rotation of the maxilla associated to the transverse movement [71].Alternatively, without pterygomaxillary separation, an inhomogeneous bone resistance existed and the V-shape opening pattern was induced by a less impediment at the anterior segments [74].A recent final element analysis stated that SARME + PD achieved a stable expansion, allowing a uniform dissipation of the distraction stresses in the craniofacial skeleton [6,7,47,62,75,76].As reported by several authors, pterygomaxillary disjunction probably does not interfere with the maxillary expansion, but it can influence the opening pattern [64,69,75].Even in the surgical approach of minimally invasive SARME, Perepérez et al. concluded that the transverse improvement at the pterygoid plates is directly related to an adequate PD [77].In terms of dentoalveolar changes, there was high evidence that a molar expansion greater than 1 mm occurred in SARME -PD compared to SARME + PD [63].This clinical finding should be interpretated considering the lower tendency of buccal molar tipping (≅ − 2 degrees) in SARME + PD, either after appliance removal or after 6 months follow-up [63].These outcomes are in accordance with several authors who described a greater expansion amount in SARME -PD, also recording a greater tendency to dental movement with the negative consequences of instability and periodontal damage [14,74,78,79].In a finite element study, De Assis et al. were able to show that the bone tension on the molars was greater when PD was not performed, and it could affect the buccal plate resorption [80].Although with high evidence, an increased buccal bone plate at premolars was found using bone-borne appliances than toothborne devices, after both SARME + PD and -PD [36].Bone-borne devices slightly decrease the tension at the molars, can limit the dental inclination, and can avoid the negative sequelae on the periodontium [74].However, the recorded buccal tipping could be the result of skeletal and dental effects [77,81].Not only the pure dental movement, but also the alveolar bone inclination due to the rotation of the maxillary segments affect the final inclination of the molars and its consequences on the adjacent tissues [77].Concerning dentoalveolar changes of the anterior teeth, high evidence showed that the amount of the anterior expansion was higher in SARME -PD than SARME + PD, according to skeletal outcomes of a V-shaped opening pattern [63].However, the intercanine transversal widening decreased between the short-and long-term followup, both for SARME + PD and -PD [63].In this review, the amount of relapse was around 1.5 mm, according to recent systematic review by Gogna and colleagues investigated the stability of SARME correction, concluding that intercanine and intermolar relapse ranged between 0.1-2.3mm and 0.23-3 mm, respectively [72].
Romano et al. measured 0.5 mm of relapse comparing CBCT before surgery, immediately after expansion, and after 6 months of follow-up, but a lack of long-term follow-up could influence their results [74].As reported in literature, after SARME it is difficult to determine whether the increase in transversal dimension is effectively due to bone widening rather than to dental movements, although a clinical improvement of breathing could be linked to skeletal effects [77,81].According to other authors, in this review no significant difference was recorded comparing nasal volume with or without PD.It's also common to detect a lower volume at the short-term follow-up compared to initial timing, considering the hemosinus induced by the surgical treatment and the expansion protocol [74,82].However, with moderate evidence, a higher NPV and OMCSA were found when PD was performed, both at shortand long-term follow-up, while the OPV increased significantly only after the active expansion [58,63].As reported by Nada et al., NPV benefits of a posterior volumetric increase at the horizontal plates of the palatine bones, occurring mainly when SARME + PD was performed [83].After removing the appliance, the decrease of OPV could be related to the tension of soft tissues, the repositioning of the tongue, and the lower reposition of the palatine plane that allows a consequent improvement of NPV.Despite the upper airway changes, to date no authors recorded a correlation between the different osteotomies of SARME and the increased airflow during breathing, considering this procedure more for orthognathic aims rather than for respiratory purpose [74,77,84].
The investigation of the best osteotomy of SARME induced also to summarize data comparing Le Fort I osteotomy with median palatal osteotomy (2S) or with two paramedian palatal osteotomies (3S).According to the segmental approach, maxillary expansion showed limited differences between 2 and 3S in terms of symmetrical pattern of opening.In contrast to these results, some studies recorded better outcomes for threesegment technique [40,[84][85][86].Landes and collegues aimed to analyze pre-and post-operative CT of 50 patients, comparing the expansion after SARME with 2S and 3S [37].No parallel expansion pattern was achieved, but 3-piece osteotomy showed more symmetric opening than bipartite technique.However, no authors reported details concerning the cut-off value beyond which an expansion should be considered unbalanced, and, like the concept of asymmetry, it should be recognized when exceeding the clinical perception [58].Despite a longer surgical treatment and a higher learning curve, Pereira et al. listed significative advantages for SARME with 3S, including greater transverse bone expansion, lower molar tipping, and lower aesthetic involvement [84].With low evidence quality, this review agreed with these results, describing a difference in terms of amount of expansion (≅ 3,5 mm TB; ≅ 0,3 mm BB) with an increased transversal width in SARME + PD and segmental 3-piece osteotomy [36].Concerning the direction of the bone movement, a lateral bending was analyzed in SARME with 2S, while a medial bending was observed in 3-piece osteotomy [36].The medial bending of the 3-piece osteotomy could limit molar inclination and periodontal complication, especially when an accurate pre-operative evaluation of the bone amount for osteotomy has been done [84,87,88].Undoubtedly, the most evident advantages of SARME with 3S were aesthetic findings, especially when incisal crowding and periodontal damage occurred.Threesegment approach avoids the increase of the nose width and the interincisal diastema that could interfere with psychological well-being and social relationships [37,40,[84][85][86].Despite the immediate benefits of SARME with 3S, it's important to highlight that this review did not record any differences in relation to skeletal stability at a long-term follow-up.With high evidence, no relapse was assessed comparing area and volume of the palate vault both in 2S and 3S surgery [58].According to these results, Senior and colleagues didn't find any difference in terms of transversal stability and complications rate between the two surgical techniques at least one-year follow-up [57].
The assessment of the best osteotomy for SARME should consider details about relapse and complications in order to define the best amount of expansion with limited side effects [58,63].According to some studies, meticulous release of all areas of increased resistance during SARME might be associated with increased postoperative discomfort [89,90].This surgical approach probably reduces the rate of asymmetric and inadequate expansion [20,43,47].In a study with 10 months follow-up, skeletal stability after maxillary expansion was ensured when the pterygomaxillary disjunction was performed [91].However, it's mandatory to highlight that this approach is more invasive and it can be associated with post-operative consequences.The studies included in this systematic review reported few data on transversal relapse according to the different surgical technique.Although some clinical studies did not record any significant differences according to specific techniques, low evidence of results doesn't allow to achieve adequate conclusions.It's advisable that future RCTs concentrate their attention on this aspect that can influence the surgical choice.
The findings of this systematic review underscore the notable stability achieved in maxillary expansion through pterygomaxillary disjunction, highlighting its central role in the clinical practice of SARME.Furthermore, the 3-piece osteotomy could be considered as crucial factor in achieving substantial aesthetic enhancements in SARME procedures.
In conclusion, the results of this systematic review should be critically analyzed.The existing moderate evidence was based on a limited number of randomized controlled trials (RCTs) within the included studies of this review.Moreover, the heterogeneity among the incorporated trials precluded a quantitative evaluation with a meta-analysis, due to the variations in result assessment.Clinical relevance was highlighted in performing pterygomaxillary disjunction to achieve more stable and homogeneous maxillary expansion with fewer side effects.In terms of segmental osteotomy, 3-piece Le Fort I might be preferred for greater expansion, limiting lateral bending of bone segments and achieving a better esthetic result.More studies are needed to confirm these results and additional research should involve randomized clinical trials to enhance methodological designs, meticulous randomization protocols, and the generation of more objective outcomes.

Fig. 1
Fig. 1 PRISMA flow diagram of the selection process

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Distance between the left and right piriform rims -Distance between jugale points bilaterally -Distance between the lateral pterygoid plates bilaterally -Angles between the left and right lateral pterygoid plates and medial pterygoid plates Dentoalveolar measurements -Distance between the canine furcation points bilaterally -Distance between the first premolar furcation points bilaterally.

Table 1
List of the included studies

; Transversal maxillary deficit (TMD) Surgical approach: osteotomy Radiographic exam; Timing of evaluation Outcomes variables Results and conclusion Methodological quality
1 (continued)

; Transversal maxillary deficit (TMD) Surgical approach: osteotomy Radiographic exam; Timing of evaluation Outcomes variables Results and conclusion Methodological quality
LowTable1 (continued)

; Transversal maxillary deficit (TMD) Surgical approach: osteotomy Radiographic exam; Timing of evaluation Outcomes variables Results and conclusion Methodological quality
GoodTable1 (continued)

Table 2
Newcastle-Ottawa quality assessment